We propose to study the logical structure of a single binary decision during the development of the cellular slime mold, Dictyostelium discoideum. We will attempt to determine the factors controlling which of two developmental pathways the cells take. During its development, a single precursor cell (the amoeba) gives rise to only two differentiated cell types (stalk cells and spores). We shall first define the two pathways by 2-D gel techniques using cell populations enriched for one or the other developmental pathway. We shall use genetic techniques to demonstrate that the putative markers do indeed comprise parts of obligatory pathways leading to the formation of each cell type. In our study of the factors controlling the expression of the two pathways, we shall continue our work on the purification and characterization of a differentiation inducing factor (DIF) we have discovered. This factor induces stalk-cell differentiation but not spores and may be cell-type specific (i.e. a morphogen). We shall be able to study its pathway specificity once we have biochemically defined the two pathways. Immunological techniques will be used to study its cellular localization and spatial distribution in the developing organism.